1. Field of the Invention
The present invention relates to methods and systems to provide surveillance, observation, and/or communication using Earth orbiting satellites. Particularly, the present invention relates to methods and systems to provide such services using on-orbit refueled satellites.
2. Description of the Related Art
A majority of satellite missions involve providing either surveillance, observation, and/or communication of (or for) Earth-based locations. Consequently, managing a satellite's relative position with the Earth is a critical factor in developing a satellite constellation configuration and orbital design. For most current satellites, the amount of thruster propellant carried by the satellite determines the operational life of the satellite. Fuel-depleted satellites are generally de-orbited or otherwise disposed. In the past, the operating assumption has been that it is less expensive to launch a new satellite than to repair or refuel an existing satellite. Thus, minimizing fuel consumption has always been an important part of satellite design and plays a key role in orbital design for the mission.
Naturally, the orbital parameters and configuration affect what can be performed by a given satellite or satellite constellation. In general, the use of high altitude orbits improves the area coverage capability and reduces the number of satellites required to achieve global coverage. Conversely, lower orbits provide better coverage resolution (e.g., observation or surveillance) for specific areas of interest.
There is a need in the art for methods and systems of satellite operations that can utilize one satellite constellation for both purposes with an optimum number of satellites for global coverage while still providing high resolution coverage to specific areas of interest with a short response time. There is further a need for such methods and systems to operate while minimizing fuel usage. As detailed hereafter, these and other needs are met by the present invention.